We have developed a method for the direct analysis of a specific simple sequence DNA in single Drosophila. We wish to extend our studies on an unusual sequence, a long pyrimidine tract (TCTCT)150 to examine the genetic variation of this simple sequence. We will characterize the biochemical properties of this same or similar sequence found in both close and distantly related species, including D. simulans, D. varians, and D. bifurca. Using new methods we have developed, we will also examine the genetic variation in this sequence that occurs within the D. melanogaster species. A new mutant which appears to have an altered satellite type DNA will be studied in more detail. A large number of strains with well characterized alterations in the kind, amount or behavior of heterochromatin will be examined for changes in this specific DNA sequence. Correlation of genetic behavior, or genetic alterations in heterochromatin, with changes in simple sequence DNA should help explain the origin, evolution and function of the repetitious DNA in constitutive heterochromatin. We hope to test a model of the evolution and function simple sequence DNA which presumes randomly occurring selectively neutral mutations in DNA.